Which material sounds better for speakers construction? Wood, Ply or MDF?

If I had time I'd love to play around with this.  I'd try routing patterns in mdf and filling them with high strength concrete.  A bag of 6,500 psi concrete costs $8 and it's hard for me to believe it couldn't be used in combination with other materials to create a great box that didn't need to cost or weigh a ton.  

The Thiel CS 7 had a concrete baffle.  There have been others.  Thiel stopped using concrete because it was too hard to ship without breaking.  I think the performance was great.  

I think it'd be an interesting challenge to build a really high performing box that was made out of cheap materials.  I'm sure it's possible, although maybe it wouldn't be practical for a manufacturer to mass produce.  MDF and concrete are cheap.  aluminum isn't all that expensive.  

@dave_b - speakers aren't the same.  Musical instruments are designed to resonate.  That's how they get their distinctive sounds.  Speakers, on the other hand, are designed not to resonate.  The less they resonate, the less of their own sound they have and the better they can reproduce the distinctive sounds of musical instruments.  

A resonant box adds distortion that is not coming from the real recording.  People like all sorts of colorations but don't imagine it's more realistic.